Oh yeah I know how this goes and it sucks big time. Lie in bed, can barely sit still and relax. Get up for a minute to go to the toilet, immediately start feeling lethargic and have difficulty keeping eyes open. Go back to bed, sleepiness goes away. In my case, anxiety medication helped.
I have had serious treatment-resistant insomnia since I was a kid and I'm also an ADHDer.
One of the things that I've found works really well for that generalised anxiety/can't unwind/can't sleep, clown will eat me sort of insomnia is clonidine. It's not for everyone but it's pretty safe and boring, it's not addictive, it's easier to get from your prescribing doctor than benzos, and it also works for treating some secondary ADHD symptoms in me as well.